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quantileDeterministic

Computes an approximate quantile of a numeric data sequence.

This function applies reservoir sampling with a reservoir size up to 8192 and deterministic algorithm of sampling. The result is deterministic. To get an exact quantile, use the quantileExact function.

When using multiple quantile* functions with different levels in a query, the internal states are not combined (that is, the query works less efficiently than it could). In this case, use the quantiles function.

Syntax

quantileDeterministic(level)(expr, determinator)

Alias: medianDeterministic.

Arguments

  • level — Level of quantile. Optional parameter. Constant floating-point number from 0 to 1. We recommend using a level value in the range of [0.01, 0.99]. Default value: 0.5. At level=0.5 the function calculates median.
  • expr — Expression over the column values resulting in numeric data types, Date or DateTime.
  • determinator — Number whose hash is used instead of a random number generator in the reservoir sampling algorithm to make the result of sampling deterministic. As a determinator you can use any deterministic positive number, for example, a user id or an event id. If the same determinator value occurs too often, the function works incorrectly.

Returned value

  • Approximate quantile of the specified level.

Type:

  • Float64 for numeric data type input.
  • Date if input values have the Date type.
  • DateTime if input values have the DateTime type.

Example

Input table:

┌─val─┐
│   1 │
│   1 │
│   2 │
│   3 │
└─────┘

Query:

SELECT quantileDeterministic(val, 1) FROM t

Result:

┌─quantileDeterministic(val, 1)─┐
│                           1.5 │
└───────────────────────────────┘

See Also